import java.util.Stack;

public class TestDemo {
    public static void main(String[] args) {
        Stack<Integer> stack = new Stack<>();
        stack.push(12);
        stack.push(23);
        stack.push(34);
        stack.push(45);
        System.out.println(stack.size());
        stack.pop();
        int ret = stack.peek();
        System.out.println(ret);
        System.out.println(stack.empty());
        System.out.println(stack.size());
        System.out.println(stack);
    }
}
